Abraham Lincoln's closest friends and confidants among his cabinet members included:

William Seward. After Seward's own presidential campaign failed, he fully gave his support to Lincoln, becoming a powerful Secretary of State under both Lincoln and his successor, Andrew Johnson. He remained one of Lincoln's closest allies throughout Lincoln's tenure.

Montgomery Blair. Lincoln's Postmaster General (1861-1864), Blair was the son of one of Lincoln's closest friends and advisors, Francis Preston Blair, a former Democrat and one of the founding fathers of the Republican Party. Lincoln accepted Montgomery Blair's resignation in 1864 (basically to appease radical Republicans), but Blair--and the Blair family--remained loyal to Lincoln.

Gideon Welles. Along with Seward, Welles remained a part of Lincoln's cabinet from the beginning until the assassination. As Secretary of the Navy, Welles helped to build up the Union fleet, which would eventually dominate the Southern coastal waters. Although Welles often clashed with Seward and Edwin Stanton (and even Lincoln), he was loyal to the President, who "nicknamed Welles his 'Neptune.' " (Wikipedia, Gideon Welles)

Edwin Stanton. Lincoln--and just about everyone else--clashed with the powerful but unpopular Secretary of War, but Stanton eventually became a close ally of Lincoln. Lincoln often decided to "plow around" Stanton, but the President recognized Stanton's usefullness. Lincoln referred to Stanton as

"... the rock on the beach of our national ocean which the breakers dash and roar, dash and roar without ceasing. He fights back angry waters and prevents them from undermining and overwhelming the land... Without him, I should be destroyed." (Wikipedia, Edwin M. Stanton)